Method of protecting wafer front pattern and method of performing double-sided process

Abstract

A wafer comprising a front surface and a back surface is provided. The wafer further includes a front pattern on the front surface, the front pattern having a plurality of holes. A low-viscosity fluid is formed on the front surface and filled into the holes. Following that, a high-viscosity fluid is formed and filled into the holes by diffusion.

1. A method of performing double-sided process capable of protecting a wafer front pattern, the method comprising:
 providing a wafer comprising a front surface and a back surface; 
 performing a front process to form a front pattern on the front surface, the front pattern having a plurality of holes; 
 forming a first photoresist solution on the front surface of the wafer, the first photoresist solution being filled into the holes; 
 forming a second photoresist solution on the front surface of the wafer, the second photoresist solution being filled into the holes by diffusion; and 
 attaching the front surface of the wafer to a supporting carrier and performing a back process on the back surface of the wafer. 
 
   
   
     2. The method of  claim 1 , further comprising performing a heating process to expel the first photoresist solution from the holes after filling the second photoresist solution into the holes. 
   
   
     3. The method of  claim 2 , wherein the heating process is performed gradually. 
   
   
     4. The method of  claim 1 , wherein the first photoresist solution has a viscosity index of between 10 and 50 centipoise (cP). 
   
   
     5. The method of  claim 1 , wherein the second photoresist solution has a viscosity index between 100 and 800 cP. 
   
   
     6. The method of  claim 1 , wherein the first photoresist solution has a smaller viscosity index than the second photoresist solution. 
   
   
     7. The method of  claim 2 , wherein the heating process further solidifies the second photoresist solution to form a protecting cap to protect the front pattern.